What it is
Glutamine is a conditionally essential amino acid: the body makes it, dietary proteins (meat, eggs, whey, casein) provide a lot of it, and intestinal and immune cells use it as fuel. Its plasma concentration drops after prolonged exercise, which gave rise to the hypothesis of an anti-infection and anti-catabolic supplement. People buy it for recovery, immunity and "intestinal permeability".
What the label does not say
- The trials on muscle mass are negative: 0.9 g/kg of lean mass per day for 6 weeks of resistance training changed nothing in strength, lean mass or protein breakdown compared with placebo (Candow 2001). The NIH sums it up: no effect on performance or body composition in adult weightlifters. Examine concludes that muscle building in healthy people has not been shown.
- The immunity argument does not hold: Gleeson (2008) reports that glutamine maintains plasma glutamine during prolonged exercise but does not prevent post-exercise immune changes, since plasma levels do not drop enough to curb lymphocyte proliferation. The reasons put forward (immunity, glycogen, anti-catabolism) have received little support from well-controlled studies in healthy adults.
- The real data concern the hospital: a Cochrane review (53 trials, 4,671 adults in intensive care) reports 21% fewer infections (RR 0.79), 3.46 fewer days in hospital and no effect on mortality, with evidence of moderate to low quality. These patients look nothing like a healthy athlete.
- The claim permitted by Health Canada is narrow: "helps to restore plasma glutamine levels after physical stress", "helps to support immune and digestive health after physical stress" and "helps in muscle cell repair after exercise", from 5 g per day. That is neither a gain in mass nor a repaired gut.
The forms on the shelf
- Free L-glutamine powder: the form used in the trials, set at 5 to 9 g per day by the Health Canada monograph.
- Glutamine from proteins and hydrolysates: Gleeson (2008) notes that athletes with a high protein intake already consume a lot of it through their proteins, hydrolysates and free amino acids.
- Solutions for patients (enteral or intravenous route): that is where the positive data are found, in adults in intensive care.
Published reference values
- Health Canada: 5 to 9 g per day in adults 18 and over; in the Workout Supplements monograph, 342.5 mg to 9 g per day, with claims from 5 g.
- Safety: 20 to 30 g as a single dose without adverse effect, 28 g per day for 14 days with no reported problem, up to 0.65 g/kg tolerated in patients (Gleeson 2008); the NIH cites 0.21 to 0.42 g/kg, or 15 to 30 g per day for 70 kg. Examine flags a rise in serum ammonia at 0.75 g/kg. No recommended intake or upper limit in the sense of the dietary reference intakes.
When
Timing has no demonstrated importance. After prolonged exercise, it raises plasma glutamine, with no measured effect on post-exercise immunity.
To mention to a professional
- Liver or kidney disease, an intestinal or immune condition for which you are considering this supplement (the hospital data fall under medical supervision), pregnancy and breastfeeding: check with a health care professional.
What it is sold for, and what the data show
Glutamine is sold for muscle recovery, athletes' immunity and "leaky gut". The trials in healthy adults who train show no gain in mass, no gain in strength and no immune protection. The documented effect on infections and length of hospital stay comes from intensive care patients fed by tube or infusion. In someone who eats enough protein, the intake is already there.
From the plate first
Every dietary protein provides it; Examine cites meats, eggs, whey and casein.
Sources
- Candow et al., Effect of glutamine supplementation combined with resistance training in young adults, European Journal of Applied Physiology 2001
- Gleeson, Dosing and efficacy of glutamine supplementation in human exercise and sport training, Journal of Nutrition 2008 (abstract read via Europe PMC)
- Cochrane, Glutamine supplementation for critically ill adults (plain language summary, 2014)
- Health Canada, natural health product monograph, Glutamine, L-
- Health Canada, natural health product monograph, Workout Supplements
- NIH Office of Dietary Supplements, Dietary Supplements for Exercise and Athletic Performance (Health Professional)
- Examine.com, Glutamine
Educational information, drawn from the sources above. It does not replace the advice of a health professional, who remains the reference for your situation, your medications, pregnancy or breastfeeding.